In dental engineering, articulators are normally used in which an upper jaw part is mounted in that the articulator cups constructed thereon are placed on vertical pegs rigid with the instrument and having spherical top ends. In their size and spacing, these pegs correspond substantially to the articulator heads, thus defining a horizontal pivot axis corresponding to the hinging axis of the temporo-maxillary joint.
Such articulators can only be used to a limited extent in performing model operations in the jaw area. In fact, it is vital to such model operations to establish whether an envisaged operative measure is leading to the desired improved occlusion of the upper and lower rows of teeth without adversely affecting the function of the temporo-maxillary joints. To this end, the best procedure is to join to each other the models produced of the upper jaw and lower jaw in the desired position of occlusion and then to check which changes in the joint area would result from such a connection. The next step is to establish which operative measures (while retaining the desired improved occlusion) would restore normal conditions in the area of the joint.
Carrying out the program which has been outlined is not possible with a conventional articulator, since with such an instrument, the interior of the articulator cups is inaccessible by reason of the articulator heads which serve for mounting the hinging axis. The description of Austrian Application A 212/87 has, however, already disclosed a way of making the area representing the articulator cups accessible from below. If the articulator cups are made from transparent material, for example acrylic glass, then it is readily possible to observe the relative movement between the articulator heads of the lower jaw model and of the fossa during pivoting of the upper jaw part of the articulator and so assess the reliability of an intended operative measure. In the initial stage of the model operation in which even greater deflections of the articulator heads of the model of the lower jaw from the desired position take place, it is not sufficient to make the articulator cups accessible from below; instead, deviations of the articulator heads upwardly must also be temporarily acceptable. This is made possible in that the temporo-maxillary joint cups are represented by a frame-like sighting area in which an arrangement of cross hairs consisting of flexible threads or the tip of a measuring rod define the desired position of the articulator heads.
The arrangement according to Austrian Published Specification A 212/87 has already proven successful for model operations in respect of the lower jaw. In this case, two-piece jaw angle templates are used, the plane of separation between the two parts corresponding to the division which takes place in sagittal lower jaw osteotomy. The two parts are shifted in respect of each other until the desired occlusion is achieved while maintaining an anatomically and physiologically viable position of the articulator heads of the lower jaw in the articulator cups.